A novel carbon fiber based porous carbon monolith

Abstract

Oak Ridge National Laboratory T.O. Box 2008 Oak Ridge. Tennessee 37831-6088 .ABSTRACT,A novel porous carbon material based on carbon fibers has been developed. The material. when activated. develops a significant micro-or mesopore volume dependent upon the carbon tiber type utilked (isonopic pitch or polyacrylonimle). The materials will find applications in the field of fluid separations or aa a catalyst support. Here. the manufacture ana characterization of our porous carbon monoliths are described. NTRODUCTIONA novel adsorbent carbon composite material has been developed'" comprising carbon fibers and a binder. The material. called carbon tiber composite molecular sieve (CFCMS), was developed through a joint research program benveen Oak Ridge Nationai Laboratory (ORNL) and the University of Kentucky, Cznter for Appiied Energy Research (UKCXER).The materials are manufactured from milled carbon fibers and powdered phenolic resin. which are slurried in water ana vacuum molded. The moiding process allows the manufacture of slabs. tubes or more complex geometries with contoured surfaces. The "green" (as molded) artifact is heated at 130°C to cure the phenolic resin and then carbonized at 650°C. Tie resultant monoliths have bulk densities in the range 0.2 -0.4 g~c m and crush strength of 1 -2 MPa. Two carbon fiber types have been utilized in our work to date.First, petroleum-pitch derived isotropic carbon fibers have been fabricated into monoliths and activated in steam or CO. at S50"C. The material develops significant microporosity, with mean pore sizes in the range 0.3 -1.0 run. and micropore volumes in the range 0.2 -0.5 cm'/g. Second monoliths have been manufacrured from polyacrylonimIe (PAN) derived carbon fibers. These materials develop significant mesoporosity in the size range 2-50 nm and mesopore volumes typically exceedins 0.5 cm'/g, making them potential catalyst support materials. In both cases the composites are strong and porous. allowing fluids to easily flow through the material.The isotropic pitch derived carbon fiber porous carbon monolith. when activated. provides a high micropore surface are3 (> 1900 m' ;g) capable o i rapid adsorption and desorption. The activated fiber microDore distribution is very narrow. with mean micropore sizes basis of molecular size and shape. . A potentially large application for our carbon-fiber based porous monoliths is gas separation using the Pressure Swing Adsorption (PSA) process. 1 nm. allowing molecular sieving on the Separation by adsorption is based on the selective accumulation of one or more components of a gas mixture on the surface of a microporous solid. When a gaseous mixture is exposed to an absorbent for sufficient time. an equilibrium is established between the adsorbed phase and the gas phase. The gas phase becomes richer in the less selectively adsorbed component. The amactive forces responsible for adsorption MASTER

Effect of Relative Humidity on Adsorption Breakthrough of CO2 on Activated Carbon Fibers

“…It is believed that KOH activation generated a high fraction of fine pores (<1 nm) [ 39 ]. The mean equivalent pore widths from Dubinin–Astakhov (DA) method were approximately 1.6 nm, corresponding to the optimum pore width for CO 2 adsorption in literature [ 40 ], though Thiruvenkatachari et al [ 41 ] reported them as 1.8 nm.…”

Post combustion CO2 capture by carbon fibre monolithic adsorbents

“…Recently, gas adsorption by activated carbon fibres and carbon fibre composites has been identified as a promising alternative. Lately, structured porous monolith materials made from carbon fibres, which have the ability to selectively adsorb gases due to their molecular sieving characteristics, have been investigated [52][53][54][55][56][57][58][59][60][61][62][63]. Carbon fibre composite in monolith form reduce inter-particle voids and maximize bulk density, thereby increasing the adsorption capacity of the material.…”

“…The manufacture of simple structures (cylindrical shape without channels or rectangular blocks) of carbon fibre composites has been previously attempted [52,57,86,109,122,101]. The fabrication process for the monolith starts with mixing the milled/ground carbon fibre and powdered phenolic resin, which is then mixed with water to form a slurry and drawn through a vacuum moulding unit to obtain the desired shape, whether it be a tube, cylinder, or other desired geometry (honeycomb in the present study).…”

“…Earlier studies showed the optimum pore width for CO 2 adsorption is about 1.6 nm (DA method) [52]. Although pore width remains an important factor in determining CO 2 adsorption, other factors such as pore volume and surface area (with CO 2 at 273 K) must also be taken into account for evaluation.…”

“…The increased CO 2 removal efficiency of coal tar pitch based composite could be attributed to favourable pore configurations (e.g. pore width 1.6 nm) for CO 2 adsorption [52] and possibly atomic, molecular forces (e.g. gas-surface interaction such as attractive van der Waals forces).…”